The present invention relates to a cell plate structure for a fuel cell, a manufacturing method thereof and a solid electrolyte type fuel cell and, more particularly, to a cell plate structure for a fuel cell wherein an electrode and a solid electrolyte layer are laminated on a porous substrate, a manufacturing method thereof, and a solid electrolyte type fuel cell employing such a cell plate structure.
In recent years, a great attention has heretofore been focused on fuel cells that generate electric power output at a high efficiency without emitting harmful exhaust gases and that serve as clean energy sources. Among these fuel cells, a solid oxide electrolyte type fuel cell (hereinafter referred to as SOFC) employs a solid electrolyte as electrolyte that achieves electrochemical reaction to provide an electric energy output.
The SOFC employs electrolyte composed of solid electrolyte with oxide ion conductivity such as stabilized zirconia added with yttria, with the electrolyte having both surfaces formed with porous electrodes to allow the solid electrolyte to serve as a partition wall whose one side is supplied with fuel gas such as hydrogen or hydrocarbon and the other side is supplied with oxidizing gas such as air or oxygen to permit the fuel cell to operate at a temperature of 1000° C.
With such a structure, the solid electrolyte has an electrical conductivity lower about by one digit number than that of the electrolyte of a phosphoric acid type fuel cell or a molten carbonate type fuel cell. In general, electrical resistance of the electrolyte portion forms a loss in electric power generation output. In order to improve an electric power generating output density, it is important form the slid electrolyte to be formed in a thin film to reduce electrical resistance of the film as low as possible.
Thus, even when, in the SOFC, the solid electrolyte is formed in the thin film as an electrolyte film, the electrolyte film layer needs a large surface area to some extent for ensuring an operating performance of the fuel cell and, hence, a cell structure with an increased mechanical strength formed with the electrolyte film is employed.
Japanese Patent Application Laid-Open Publication No. H5-36417 and Japanese Patent Application Laid-Open Publication No. H9-50812 respectively disclose structures wherein a plate-like or hollow substrate composed of either one of electrodes, i.e. air electrode material is formed with a solid electrolyte layer and a fuel electrode, which forms either one of the electrodes, in sequence, such as a structure wherein the substrate, supporting the solid electrolyte, also serves as the other electrode.
European SOFC Forum (issued in 2000), on pages 231 to 240, describes so-called electric power generating three layers (a first electrode layer/a solid electrolyte layer/and a second electrode layer) formed on the porous metallic substrate by thermal plasma spraying method.